Electrical insulator assembly with oxygen permeation barrier

Abstract

A high-voltage electrical insulator (21) for electrically insulating a thermoelectric module (17) in a spacecraft from a niobium-1% zirconium alloy wall (11) of a heat exchanger (13) filled with liquid lithium (16) while providing good thermal conductivity between the heat exchanger and the thermoelectric module. The insulator (21) has a single crystal alumina layer (SxAl 2 O 3 , sapphire) with a niobium foil layer (32) bonded thereto on the surface of the alumina crystal (26) facing the heat exchanger wall (11), and a molybdenum layer (31) bonded to the niobium layer (32) to act as an oxygen permeation barrier to preclude the oxygen depleting effects of the lithium from causing undesirable niobium-aluminum intermetallic layers near the alumina-niobium interface.

We claim: 
     
       1. A high voltage insulator having high thermal conductance and adapted to be placed in contact with a heat exchanger having an oxygen-permeable refractory metal container or wall with liquid lithium therein, said insulator including: a single crystal alumina layer a surface adapted to face towards said refractory metal container when said insulator is in contact therewith,   a niobium layer on said surface of said alumina layer,   an oxygen permeation barrier layer covering said niobium layer, said barrier layer having a low oxygen permeability, a high thermal conductance, a high melting point, a thermal expansion coefficient close to that of niobium and a slow interdiffusion with niobium.   
     
     
       2. A high-voltage insulator as set forth in claim 1, wherein said barrier layer is a metal selected from the groups of molybdenum, rhenium, iridium and platinum. 
     
     
       3. A high-voltage insulator as set forth in claim 1, wherein said barrier layer has complete solid-solid miscibility with niobium. 
     
     
       4. A high-voltage insulator as set forth in claim 3, wherein said barrier layer is molybdenum. 
     
     
       5. A high-voltage insulator as set forth in claim 1, and further including a second niobium layer on the surface of said single crystal alumina layer which is adapted to face away from said heat exchanger when said insulator is in contact therewith, and a second oxygen permeation barrier covering said second niobium layer, both of said niobium layers having the same thickness, and both of said oxygen permeation barriers being of the same material and of the same thickness. 
     
     
       6. A high-voltage insulator as set forth in claim 5, wherein each of said barrier layers is a metal selected from the groups of molybdenum, rhenium, iridium and platinum. 
     
     
       7. A high-voltage insulator as set forth in claim 5, wherein each of said barrier layers has complete solid-solid miscibility with niobium. 
     
     
       8. A high-voltage insulator as set forth in claim 7, wherein each of said barrier layers is molybdenum.